错配修复蛋白MSH2调控跨损伤DNA合成与疾病发生研究

Translesion DNA synthesis (TLS) can limit the production of DNA double-strand breaks and cell death by utilizing specialized DNA polymerases which have low fidelity to insert and/or extend nucleotides across lesions in genome. A best example is that Polη can bypass UV-induced CPD lesions correctly and efficiently, whose deficiency leads to a high mutation rate and skin tumors. Given their low fidelity when copy undamaged templates in vitro, it is believed that in vivo TLS process is strictly regulated. Recently, we found in surprise that MSH2, an important mismatch repair protein, can regulate PCNA monoubiquitination and TLS polymerase recruitment after UV irradiation. We will combine multiple cellular, biochemical & molecular techniques to explore the regulation mechanism of MSH2 on PCNA monoubiquitination and Polη function after UV irradiation in detail. We will also clarify whether Polη dysfunction caused by MSH2 mutations is related to the skin tumor development in some colon cancer patients. We believe these results will not only provide clues to the underlying mechanisms about genome variations, but also help us clarify the interplay among multiple pathways in DNA damage response, which will be important for understanding carcinogenesis and finding strategies to reduce its risk.

跨损伤DNA合成（TLS）能利用特异的低保真度DNA 聚合酶在损伤DNA加合物对侧复制DNA，避免细胞产生DNA双链断裂甚至死亡。已知聚合酶Polη能正确复制紫外辐射产生的CPD加合物，缺失Polη使细胞的紫外突变率和皮肤癌发生率显著上升。然而由于TLS聚合酶在复制未损伤模板时的低保真性，体内TLS过程受到严格调控。我们最近研究意外发现错配修复关键分子MSH2能调控UV辐射诱发的PCNA单泛素化和TLS聚合酶招募。在本项目中，我们将应用多种分子和细胞生物学技术、结合临床样本，深入研究MSH2调控紫外辐射后PCNA单泛素化以及Polη功能的机制，探讨MSH2突变导致的Polη功能异常与疾病发生相关性。结果将有助于阐明基因组变异发生机制、明确多种DNA损伤应答通路之间的相互作用，对于深入理解癌症发生和进行肿瘤防治提供重要的理论基础。

跨损伤DNA合成（TLS）通路能利用特异的低保真度DNA 聚合酶在损伤DNA加合物对侧复制DNA，避免细胞产生DNA双链断裂甚至死亡。已知TLS聚合酶Polη能正确复制紫外辐射产生的CPD加合物、抑制皮肤癌发生。我们发现错配修复蛋白MSH2与Polη结合，促进紫外辐射后PCNA单泛素化、Polη到损伤位点的募集和细胞复制CPD加合物的能力。MSH2调控PCNA单泛素化是通过影响RAD18和RPA32的招募来实现的，该调控不依赖于细胞周期和错配修复。我们也发现MSH2互作蛋白REV1、SART3和Parkin也与Polη结合，通过不同机制调控RAD18的招募和PCNA单泛素化。另外，我们还发现Muir-Torre综合症相关的两个MSH2突变体干扰了紫外辐射后Polη的招募，表明这些MSH2突变很可能干扰了细胞保真性复制CPD加合物，促进基因组变异和皮肤癌的发生。这些发现有助于我们深入理解TLS通路的调控，为预防皮肤癌发生以及以TLS通路作为肿瘤耐药性药物靶标提供了重要的理论基础。目前已经发表与该项目相关的SCI 文章17 篇，包括Nature Commun (2017)、Nucleic Acids Res (2015，2017a,b，2018)、PloS Biol (2016)、J Cell Sci (2016)等。

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